The present invention relates to an optical apparatus for driving a focusing optical element to the focus position according to the movement of a variable power optical element (that is, according to variations in focal distance).
The driving mechanism for a focusing optical element in the driving mechanism of a variable power optical system comprises, as in the focal length adjusting apparatus disclosed in the Japanese Patent No. 2,856,557, a first lens unit, a second lens unit, a motor for moving the second lens unit with respect to the first lens unit, moving means for moving the first and the second lens units and the motor in the direction of the optical axis as a single unit, detecting means for detecting the stop position of the first lens unit to be moved by the moving means, and determining means for determining the moved position of the second lens unit to be moved by the motor with respect to the first lens unit according to the result detected by the detecting means.
A general construction of the embodiment disclosed in the Japanese Patent No. 2,856,557 is shown in FIG. 8 and FIG. 9.
Part A of FIG. 8 shows the general construction of a camera according to an embodiment described above, and part B of FIG. 8 shows the extended position of each optical element at a prescribed zoom position. FIG. 9 shows a sequence of focusing operations in the camera of the embodiment described above.
In Part A in FIG. 8, the reference numeral L301 designates a first lens unit, the reference numeral 303 designates a lens-barrel of a first group, the reference numeral L302 designates a second lens unit, and the reference numeral 308 designates a lens-barrel of a second group. The reference numeral L303 designates a third lens unit.
The reference numeral 304 designates a cam pin of the first group provided around the outer periphery of the lens-barrel 303 of the first group, the cam pin 304 of the first group engages a cam groove of the first group formed on a rotatable cam cylinder 305 of the first group on the outer peripheral side of the lens-barrel 303 of the first group. The lens-barrel 303 of the first group is linearly guided by a linear guide member. Therefore, when the rotatable cam cylinder 305 of the first group rotates, the lens-barrel 303 of the first group is linearly driven in the direction of the optical axis by engagement between the cam groove of the first group and the cam pin 304 of the first group.
The reference numeral 306 designates a cam barrel of the second group, which is disposed inside the lens-barrel 303 of the first group. A cam pin 309 of the second group provided on the outer peripheral surface of the lens-barrel 308 of the second group engages a cam groove of the second group formed on the cam barrel 306 of the second group. In the cam barrel 306 of the second group, a drive pin 307 is provided, which passes through an elongated hole formed so as to extend in the circumferential direction on the lens-barrel 303 of the first group and engages the linearly guiding elongated hole formed so as to extend in the direction of the optical axis on the rotatable cam barrel 305 of the first group.
Therefore, the cam barrel 306 of the second group rotates in the same phase with the cam barrel 305 of the first group, and moves in the direction of the optical axis together with the lens-barrel 303 of the first group. When the cam barrel 306 of the second group rotates, the lens-barrel 308 of the second group is driven in the direction of the optical axis by engagement between the cam groove of the second group and the cam pin 309 of the second group, and then is linearly driven in the direction of the optical axis by the amount added with the distance moved of the cam barrel 306 of the second group in the direction of the optical axis.
The reference numeral 310 designates a drive unit for focusing for driving the third lens unit L303 in the direction of the optical axis, and is mounted on the bottom board of the second group fixed on the lens-barrel 308 of the second group.
The reference numeral 311 designates a power zoom driving unit comprising a motor and a decelerator for rotating the cam barrel 305 of the first group.
The reference numeral 312 designates a fixed cylinder, which also serves as a body of the apparatus for rotatably supporting the cam barrel 305 of the first group, and the reference numeral 313 designates a photosensitive member such as film, a solid-state imaging device or the like supported by the fixed lens barrel 312.
The reference numeral 314 designates an amplifier for amplifying the detected signal from a photodetector 301 described later, and the reference numeral 315 designates a distance measuring circuit. The reference numeral 316 designates a microcomputer, and the reference numeral 317 designates a drive circuit for focusing, which controls the drive unit for focusing 310. The reference numeral 318 designates an outer covering provided with the operating members such as a release switch, a zoom switch, or the like.
The photodetector 301 is fixed on the bottom board of the second group described above to be driven with the lens-barrel 308 of the second group as a single unit. The photodetector 301 comprises, as shown in FIG. 10, an infrared radiation floodlighting element 301a facing toward the entrance surface of a prism 302 held by the lens-barrel 303 of the first group, and a light receiving element portion 301b facing toward a slit plate 302a provided on the side of the projecting surface of the prism 302.
The infrared radiation emitted from the floodlighting element 301a is reflected by a reflecting surface 302d of the prism 302, and a portion of reflected light passed through the slit formed on the slit plate 302a is thrown on the light receiving element portion 301b as slit light. On the light receiving element portion 301b, two slit-shaped light receiving areas 301c, 301d are formed.
In the slit plate 302a, as shown in FIG. 11, slit rows S1 and S2 extend in parallel in the direction of the optical axis and are disposed so as to be orthogonal to the optical axis. Slit light passed through the slits in the row S1 is received in the light receiving area 301c and slit light passed through the slits in the row S2 is received in the light receiving area 301d. 
In the row S1, the slits are formed at a regular pitch P1 in the direction of the optical axis, and a distance D between the slits of both ends of the row S1 is the same as the maximum value of the relative distance moved between the first lens unit L301 and the second lens unit L302.
On the other hand, each slit in the row S2 is displaced by an amount Z1 with respect to the corresponding slit in the row S1 except for the slit located at the center. The amount of displacement Z1 is the same for all the slits except for the slits on both ends of the row S2, and the direction of displacement is counterbraced. A displacement amount Z2 of the slits located on both ends of the row S2 is larger than Z1. The driving direction of the first lens unit L1 can be detected by the direction of displacement of the slit.
The position of the second lens unit L302 with respect to the first lens unit L301 (zoom position) can be detected by reading the amount of displacement described above from the output difference between the light receiving areas 301c and 301d. 
More specifically, the photodetector 301 moves in the direction of the optical axis with respect to the prism 302 and the slit plate 302a together with the second lens unit L302, and wave shaped signals as shown in FIG. 12 are fed from the photodetector 301 every time the photodetector 301 passes over pairs of slits of the rows S1 and S2. The level of the signal of the photodetector 301 at the moment when the photodetector 301 is positioned at the center of the pairs of slits of the rows S1 and S2 is regulated to be a half the maximum output value thereof at each zoom position.
When the zoom positions shown by C1-Cn in FIG. 13 are specified by the operation of the zoom switch, the microcomputer 316 drives the first and the second lens units L301 and L302 via the power zoom driving unit 311. Every time the photodetector 301 reaches the position where a half the maximum output signal value is fed together with the second lens unit L302, a comparator feeds the signal, and at the moment when the count value of this signal becomes equal to the value of the specified zoom position n, the microcomputer 316 stops driving the first and the second lens units L301 and L302.
The positional relation between the first and the second lens units L301 and L302 at each zoom position is shown in FIG. 13.
When such a zooming operation is carried out, the microcomputer 316 calculates the position of the second lens unit L302 and the focus position where the third lens unit L303 should be driven based on the distance to the object measured by the distance measuring circuit 315 to move the third lens unit L303 to the focus position via the drive unit for focusing 310.
The focusing operation of the lens in the apparatus of such a structure will be described using a flow chart of part B in FIG. 8 and FIG. 9.
Part B in FIG. 8, the reference numeral 319 shows a position of the first lens unit L301 in the direction of the optical axis according to the zooming operation. The reference numeral 320 shows a position of the second lens unit L302 in the direction of the optical axis according to the zooming operation. In addition, the reference numeral 321 shows a position (focus position) of the third lens unit L303 in the direction of the optical axis corresponding to the zooming position with the object positioned at a prescribed distance.
Part B in FIG. 8 shows a state in which a position f0 is a zoom position, the focal distance of which is f0, and the photodetector 301 is positioned at the center of the pair of the slits (corresponding to the position C4 shown by the dotted line in FIG. 13, for example).
Assuming that the zooming operation is terminated and the first and second lens units L301, L302 are stopped at a focal distance f1 that is displaced from the focal distance f0 by xcex94Zp. Such a displacement of the stopped position occurs due to an operational response lag from the moment when the count value of the output signals from the comparator described above becomes equal to the value of the specified zoom position n until the first and the second lens units L301, L302 are actually stopped, or due to mechanical rattling.
When the release switch is operated in this state (step #1 in FIG. 9), the distance moved by the third lens unit L303 for focusing is calculated.
The microcomputer 316 calculates the amount of displacement of the zoom stop position from the center xcex94Zp using the output of the photodetector 301 (step #2, #3).
As a next step, the reference distance moved xcex94x0 for obtaining the focus position of the third lens unit L303 with the object located at a prescribed distance as described above in the case where the second lens unit L302 is positioned at the center of a zoom position Zp is read from a ROM and expressed as xcex94x (step #4, #5).
Then, the distance D to the object is measured using the distance measuring circuit 315, and xcex94F(1/D) or the distance moved corresponding to the reciprocal of the distance to the object D is obtained from the ROM of the microcomputer 316, and then the value of xcex94x added to xcex94F(1/D) is expressed as xcex94x (step #6, #7, #8).
Subsequently, information on the offset xcex94x2 (xcex94Zp) of the distance moved of the third lens unit L303 corresponding to the displacement information of the zoom stop position xcex94Zp is read from the ROM (step#9). Then the value of xcex94x added to xcex94x2 (xcex94Zp) is expressed as xcex94x (step#10).
By this process, the distance moved of the third lens unit L303 at the focal length f1 calculated by the expression;
xcex94x1=xcex94x0+xcex94F(1/D)+xcex94x2(xcex94Zp)
is obtained, and the microcomputer 316 drives the third lens unit L303 to the focus position by this distance moved (step#11).
In this way, according to the embodiment described above, the difference (xcex94Zp) between the reference position (focal length f0) and the position where the first and the second lens units L301, L302 are actually stopped (focal length f1) is detected at each zoom position, so that the position of the third lens unit L303 is determined.
In other words, the detection accuracy of the displacement positions where the first and the second lens units L301, L302 are actually stopped xcex94Zp from the reference zoom position affects the accuracy of the position of the third lens unit L303 to a large extent.
In addition, the zoom mechanism disclosed in Japanese Patent No. 2,505,192 comprises a focusing lens holding frame, a variable power lens holding frame, detecting means for detecting the position of the variable power lens holding frame, a storing unit for storing the distance moved of the focusing lens holding frame with respect to the distance moved of the variable power lens, and control means for converting the position of the variable power lens holding frame detected by the detecting means described above into the output corresponding to the distance moved of the focusing lens holding frame stored in the storing unit to move the focusing lens holding frame with respect to the variable power lens holding frame.
In this zoom mechanism as well, as in the case of the focal length adjusting apparatus disclosed in Japanese Patent No. 2,856,557, the detection accuracy of the detecting means for detecting the position of the variable power lens holding frame affects the accuracy of the position of the focusing lens holding frame to a large extent.
In order to detect the displacement xcex94Zp of the reference zoom position from the position where the lens was actually stopped, the movable body detecting apparatus proposed in Japanese Unexamined Patent Application Publication No. 8-94903 is also used in addition to the photodetector shown in the embodiment in Japanese Patent No. 2,856,557.
As shown above, in order to increase the accuracy of the focus position of the focusing optical element, it is necessary to increase the accuracy of detection of displacement between the reference zoom position and the position where the variable power optical element is actually stopped. In addition, there is a tendency that miniaturization or increases in focusing sensitivity of the optical system increase the accuracy of the focus position required by the focusing optical element.
Therefore, for example, in the movable body detecting apparatus proposed in Japanese Unexamined Patent Application Publication No. 8-94903, the profile irregularity of the surface of the resistive element is improved to improve the accuracy of displacement detection between the reference zoom position and the position where the lens is actually stopped.
However, such an apparatus for detecting the position at high accuracy is expensive. In addition, miniaturization of or increase in focusing sensitivity of the optical system requires detecting accuracy greater than the limit of the conventional position detecting apparatus.
Accordingly, it is an object of the present invention to provide a lens control apparatus that can perform a focusing operation with high accuracy in association with a zooming operation while using less expensive position detecting means.
An aspect of the present invention is a lens position control apparatus comprising a variable power lens unit that moves along an optical axis; a focusing lens unit; a drive unit which drives the variable power lens unit along the optical axis; a member which defines the reference position to be used for calculating a driven amount of the focusing lens unit in association with the focusing operation thereof; and a linking member which links the member and the variable power lens, wherein the member moves along the optical axis in accordance with variable power lens unit through the linking member.
The lens position control apparatus of the present invention further comprises a focus lens drive unit which drives the focusing lens unit, and the focus lens drive unit drives the focusing lens unit toward the reference position prior to the focusing operation.
Especially, the focus lens drive unit drives the focusing lens unit based on the driven amount described above after the focusing lens unit reaches the reference position.
In addition, the variable power lens drive unit comprises a rotatable cam barrel, and the cam barrel is provided with cam grooves for moving the variable power lens unit and the member.
The lens position control apparatus of the present invention further comprises a position detecting unit which detects the cam position of the cam barrel, a distance detecting unit which detects the distance to the object, and a calculating unit which calculates the driven amount of the focusing lens unit from the reference position in association with the focusing operation thereof; and the calculating unit calculates the driven amount described above based on the position signal from the position detecting unit and the distance signal from the distance detecting unit.
The lens position control apparatus of the present invention further comprises a position detecting unit which detects the position of the variable lens unit, a distance detecting unit which detects the distance to the object, and a calculating unit which calculates the driven amount of the focusing lens unit from the reference position in association with the focusing operation thereof; and the calculating unit calculates the driven amount described above based on the position signal from the position detecting unit and the distance signal from the distance detecting unit.
The reference position of the member is a position corresponding to a prescribed distance to the object.
The prescribed distance to the object is an infinite distance to the object.
The focusing lens unit comprises a detecting section for detecting the reference position of the member.
The further characteristics of the present invention will be apparent from the description of the drawings.